The present invention relates to a nitride semiconductor substrate to be used as a substrate for a blue light-emitting diode or a blue semiconductor laser device or the like, a method of manufacturing the semiconductor substrate, a semiconductor device employing the nitride semiconductor substrate, and a pattern forming method for the manufacture of the semiconductor device.
Conventionally, semiconductor devices such as a blue light-emitting diode (blue LED) or a blue semiconductor laser device employing a group III nitride such as GaN (gallium nitride), InN (indium nitride), AlN (aluminum nitride), or their mixed crystals, have been in most cases formed on a sapphire substrate.
In the manufacturing process of the semiconductor devices employing the nitride semiconductor, particularly in the manufacturing process of semiconductor laser devices, registration errors on the order of 1 μm do not pose any practical problems. Accordingly, a sufficient registration accuracy can be ensured by using inexpensive exposure apparatus (costing about ten thousand yen per unit) using g-line (wavelength 436 nm) or i-line (wavelength 365 nm) of a mercury lamp, instead of the expensive KrF steppers (costing several billion yen per unit), which are used in the photolithography process for Si (silicon).
However, there was a problem that with an increasing use of a nitride semiconductor substrate as a substrate for the semiconductor device, the accuracy of the resist pattern (hereinafter referred to as a pattern accuracy) drops in the photolithography step during the formation of the semiconductor device, particularly when the pattern is formed by the exposure apparatus using the g- or i-line of the mercury lamp, thereby significantly lowering the yield of the semiconductor device.